1. Field of the Invention
This invention relates to a laminated structure. More particularly, this invention relates to a laminated structure provided with pairs of corresponding bumps or conjunction portions which are electrically connected to each other by particles embedded.
2. Description of Prior Art
ACF (Anisotropic Conductive Film) is a conductive film composed of epoxy resin and a plurality of metal particles and is often used as interlayer clamped between two corresponding bumps or electrodes of a substrate and LSI (Large Scale Integrated Circuit), COG (Chip On Glass), FPC (Flexible Printed Circuit), PCB (Printed Circuit Board), TAB (Tape Automatic Bonding) or TCP (Tape Carrier Package) so as to form a laminated structure for use in LCD panels.
However, two adjacent bumps or electrodes of the substrate can easily short-circuit or suffer low conductivity when the laminated structure is bent, causing the particles in the ACF that are located between two electrodes, to crowd together.
Further, the manufacturing process of ACF is complicated, and the tolerance of the height difference among the bumps of LSI/FPC/PCB/TCP cannot always be precisely controlled. If the design aims to increase the amount of conductive particles captured by the bumps or electrodes, the size of the bumps or electrodes formed on the LSI/FPC/PCB/TCP cannot be too small to contact the conductive particles within the predetermined area. If the design aims to increase the conductivity between two corresponding bumps or electrodes by increasing the number of particles in the ACF, the effective space (Fine Pitch Design) between any two of the adjacent bumps or electrodes cannot be so narrow as to cause a short circuit.
FIGS. 1A, 1B and 1C are three plan views sequentially depicting the steps for forming a laminated structure 1 according to a prior art. The substrate 11, 12 are two conductive plates of LSI/COG/FPC/PCB/TAB/TCP.
As shown in FIG. 1A, the laminated structure 1 is composed of two substrates 11(12), a plurality of conductive particles 13 and an epoxy 14. The substrate 11 has a surface 110 with a plurality of spaced bumps A1xcx9cA3, and the substrate 12 has a surface 120 with a plurality of spaced bumps (B1xcx9cB3) corresponding to bumps A1xcx9cA3. The so-called Anisotropic Conductive Film (ACF) is made of epoxy 14 mixed with the particles 13, and the ACF is used as an intermediate to bond the substrates 11 and the substrates 12 together and electrically connect the substrates 11 to the substrates 12. The bumps A1xcx9cA3 of the substrate 11 are respectively provided with end surfaces A01, A02 and A03, and the bumps B1xcx9cB3 of the substrate 12 are respectively provided with end surfaces B01, B02 and B03. A height difference t1 exists between the bump B1 and the bump B2, and another height difference t2 exists between bump B2 and bump B3.
FIG. 1B shows the substrate 11 and the substrate 12 being brought toward each other by the application of a clamping force F. FIG. 1C shows the first substrate 21 and the second substrate 22 being combined together by the epoxy 14 and electrically connected to each other via the particles 13.
In FIG. 1B, a force F is applied on the two substrates 11, 12 to form the laminated structure 1. The epoxy 14 is gradually deformed and thinned by the approaching substrates 11 and 12, and then the particles 13 stored in the epoxy 14 are irregularly dispersed during the clamping process. Then, the bump A1 and the bump B1, the bump A2 and the bump B2, the bump A3 and the bump B3 respectively clamp the particles 13 stored in the epoxy 14 as shown in FIG. 1C.
However, with the height differences t1 and t2 between bump B2 and bump B1, B2, the number of the particles 13 clamped between each two corresponding bumps is quite different, i.e. the particles 13 are not easily captured by the any two corresponding bumps. Moreover, a short circuit may occur between any two of the bumps of the substrate 11 or 12 between which the number of the particles 13 is dense.
U.S. Pat. No. 5,065,505 disclosed by Hiroshi Matsubara et al, Sharp Kabushiki Kaisha, mentions that the conductive particles are adhered to the electrodes of the glass board by means of the uncured photocuring adhesive. However, height differences existing among the electrodes cannot be effectively compensated while the circuit board is connected to the electrodes of the glass board.
The primary object of this invention is to provide a laminated structure, comprising a first substrate, a second substrate, an intermediate and a plurality of particles. The first substrate has a first conjunction portion and a second conjunction portion, and the second substrate has a third conjunction portion and a fourth conjunction portion which are provided with a first hardness. The intermediate is disposed between the first substrate and the second substrate. The particles with a second hardness larger than the first hardness are coated on the third conjunction portion for contacting the first conjunction portion and coated on the fourth conjunction portion for contacting the second conjunction portion. A height difference with reference to the base surface of the second substrate exists between the end surface of the third conjunction portion and the end surface of the fourth conjunction portion.
A height difference is exists between the fourth conjunction portion and the third conjunction portion and the height of the fourth conjunction portion is presupposed lower than that of the third conjunction portion. The height difference can be compensated by the particles embedded in the fourth conjunction portion when a clamping force is applied, and therefore the junction between the third conjunction portion and the first conjunction portion can be uniformly bridged by the particles located therebetween.